1. Field of the Invention
The present invention relates to an optical apparatus including an image pickup lens and an image pickup apparatus.
2. Description of the Related Art
In an image pickup apparatus, such as a video camera and a still camera, an operating member is usually disposed to perform, for example, a zooming operation to change the zoom ratio of an optical system and a manual focusing operation to manually adjust the focus on a subject. The zoom ratio and the focus state of the optical system can be changed by moving, among lens groups constituting the optical system, a variator lens group (also called a zoom lens) and a focusing lens group (also called a focus lens) in the direction of light axis of the optical system.
The operating member for moving the lens with the zooming operation and the manual focusing operation is constituted by an operating ring fitted around a lens barrel. A rotation of the operating ring is converted to linear movements of the lens through a mechanical cam mechanism. Recently, however, a power-zoom/power-focus mechanism for electrically driving the lens by a motor has been used in many cases. In that case, the operating member is constituted by an electronic ring, a volume key, and/or a switch, and an operation input from the operating member is converted to an electric signal. A microcomputer incorporated in, e.g., a camera body detects the converted electric signal and controls the motor to perform zoom driving and manual focus driving. Such an arrangement eliminates the need of a complicated cam mechanism and enables the operating member to be disposed in a desired position. Therefore, reduction in both size and cost of the lens and the camera can be realized.
When the operating member is an electronic ring, an operation input from the operating member can be detected based on rotation of the electronic ring, and when the operating member is a volume key, an operation input from the operating member can be detected based on pressure applied to depress the volume key. In general, therefore, the electronic ring can realize finer detection of the operation input applied from a user and can provide more excellent operability than the volume key. On the other hand, a switch is inferior to the other types of operating members in operability because it is just able to detect an on- or off-state. Because the volume key and the switch are inexpensive and small in size, they are often used in relatively low-price cameras. While the electronic ring is more costly and larger in size, it is able to easily perform fine operation and to give the user an operation that is close to that in the case using the mechanical cam mechanism. For that reason, the electronic ring has greater demands among the experienced persons and is used in middle- and higher-class cameras. However, when the user holds a camera by hands, both the hands are required; namely one hand holds the camera and the other hand operates the electronic ring. In many of cameras mounting the electronic rings, therefore, the volume key or the switch is also separately disposed near a camera grip so that, though deterioration in operability, the camera can be operated by one hand while holding it.
The known techniques for the power-zoom/power-focus control will be described below. Since the zooming operation and the manual focusing operation are the same in point of controlling a lens position in accordance with an operation applied from the user, the following description is made of the zooming operation as a typical example.
In one of the known techniques for realizing the zooming operation with the electronic ring, an electric signal generated with the rotation of the electronic ring is detected and the speed of a zoom lens is controlled in accordance with the detected electric signal (see Patent Document 1; Japanese Patent Laid-Open No. 9-243899). The technique for detecting the electric signal generated with the rotation of the electronic ring is divided into the absolute value type outputting an absolute angle of the rotational position of the electronic ring, and the relative value type outputting a relative rotational angle of the electronic ring. One example of the absolute value type is to output a voltage in proportion to a rotational angle (also simply called an angle) of the electronic ring by using a variable resistance. Examples of the relative value type outputting the relative rotational angle include a type outputting an on- or off-pulse each time when the electronic ring is rotated through a predetermined angle, and a type outputting a cyclically changing voltage per a predetermined angle. The former type is realized with, e.g., a photointerrupter, and the latter type is realized with, e.g., a magnetic resistance (MR) device (detail description of those techniques are omitted here).
The electronic ring of the absolute value type is superior to the relative value type in point of providing the absolute angle, but it is disadvantageous in having a relatively high cost and being difficult to increase resolution in angle detection. On the other hand, the relative value type electronic ring cannot provide the absolute value, but it is relatively inexpensive and can provide high resolution. For those reasons, the relative value type electronic ring is widely used.
Hitherto, as disclosed in Patent Document 1, the zooming operation by the electronic ring has been performed through the steps of detecting the amount of rotation of the electronic ring per unit time by a microcomputer, converting the detected amount of rotation to data representing the moving speed of a zoom lens, and controlling a zoom motor in accordance with the converted data. More specifically, when the electronic ring is rotated at a high speed, the zoom driving is quickly performed, and when the electronic ring is rotated at a low speed, the zoom driving is slowly performed.
With such an arrangement as enabling the zooming operation to be performed by the electronic ring through the power zoom control, a low-cost and compact image pickup lens and image pickup apparatus can be realized without using the complicated cam mechanism.
However, the above-described known techniques have problems as follows.
First, because the zoom speed is a control parameter representing the operation applied from the user operating the electronic ring, the rotational angle of the electronic ring is not matched with the zooming position, i.e., optical magnification. Even with the electronic ring rotated through the same angle, therefore, the optical magnification is, e.g., five times when the electronic ring is quickly rotated, while it is, e.g., two times when the electronic ring is slowly rotated. In the lens using the mechanical cam mechanism, since the ring rotational angle and the optical magnification correspond to each other in a 1:1 relation, the user can operate the lens in an intuitively fit manner. However, the known electronic ring cannot realize the intuitively fit operation and it is poor in operability.
Secondly, in the case of the zoom motor having a limit in speed, the zoom motor cannot be driven at a speed over the limit even when the electronic ring is rotated as quickly as possible. For example, when a stepping motor is used as the zoom motor, an upper limit has to be set in motor rotational speed to avoid an out-of-synchronism phenomenon that the motor cannot rotate at a predetermined speed or higher. With the setting of such an upper limit, in the case of a lens requiring, e.g., 2 seconds to move from the wide-angle side (wide end) to the telephoto side (tele end) even at a maximum driving speed, the lens cannot be moved from the wide end to the tele-end unless the electronic ring is continued to be rotated at least for 2 seconds. Accordingly, the amount of input operation required for the electronic ring is increased. In photographing with cameras, the optical magnification is often desired to be changed at a stroke. The lens using the mechanical cam mechanism is adaptable for such a demand because the lens can be moved from the wide end to the tele end by manually rotating the ring through a predetermined angle. As compared with that lens, the lens using the known electronic ring is inferior because the operating member requires a larger amount of input operation.
The above-described two problems are attributable to the arrangement that the moving speed of the zoom lens is controlled in accordance with the amount of input operation of the operating member. As an alternative, the arrangement may be modified such that an absolute position of the zoom lens is controlled in accordance with the amount of input operation of the operating member, i.e., that the zooming position is controlled in a 1:1 relation between an absolute angle of the electronic ring and an absolute position of the zoom lens. Such a solution should be able to realize a feel in operation comparable to that in the image pickup lens using the mechanical cam mechanism.
However, when the electronic ring of the relative value type is used as the electronic ring, information of only the relative rotational angle is obtained and control for making the absolute angle of the electronic ring and the absolute position of the zoom lens correspondent to each other in a 1:1 relation is difficult to realize. On the other hand, when the electronic ring of the absolute value type is used, information of the absolute rotational angle of the electronic ring is obtained and therefore the above-mentioned control can be more easily realized. Even in that case, however, the following problem is caused in addition to the higher cost and lower resolution of the electronic ring of the absolute value type.
In many of cameras mounting the electronic rings of the absolute angle type, the volume key is also disposed near the camera grip in addition to the electronic ring, as described above, so that the zooming operation can be performed by any of the electronic ring and the volume key. Further, the zooming operation can also be often made feasible by a device, e.g., a remote controller, other the operating member mounted on a camera body. In the case of such a device being used in combination with the electronic ring, when the position of the zoom lens is moved by the device, only the zoom lens position is changed while the angle of the electronic ring is kept the same. This raises the problem that the 1:1 correspondence between the absolute angle of the electronic ring and the absolute position of the zoom lens is lost.
With one known method for reducing the problem that the 1:1 correspondence is lost, a driving device is disposed to drive the electronic ring such that the electronic ring is also automatically rotated when the zooming position is changed by a device other than the electronic ring, thereby keeping constant the positional relationship between the electronic ring and the zoom lens. However, the one known method raises the problems that a mechanism required for the electronic ring becomes very complicated, the cost is increased, and reliability is reduced with the more complicated mechanism. With another known method, a switch for switching over an effective mode and an ineffective mode of the electronic ring operation is disposed such that the electronic ring and the other means are controlled to be exclusively used. When the electronic ring is made effective, the zoom lens is automatically moved to a position corresponding to the absolute angle of the electronic ring, thereby keeping the constant positional relationship therebetween. However, the other known method raises the problems that the switching operation using the switch is troublesome, and when the electronic ring is made effective, the zooming position is unintentionally changed.
Thus, with the known techniques and methods, even when the electronic ring of the absolute value type is used with intent to perform the control for holding the absolute angle of the electronic ring and the absolute position of the zoom lens in the 1:1 correspondence, an improvement in operability of the zooming operation is not always ensured.